Auto Research Corporation

August X Sidler

Carl H Smith

Fluid pressure sensing means for sensing lubricant pressure levels. Means are activated to turn on a pump at regular intervals to provide lubrication at such intervals. It is desired to indicate failure of subsequent operation of the pump after a time interval greater in duration than the aforesaid periodic intervals. Pump operation causes closure of pressure switch which causes capacitance means to charge during the switch closure interval. As soon as the capacitance is charged beyond a predetermined threshold level, bistable means are set which in turn sets up a discharge path for the capacitor. The long-time constant of the discharge path, which is adjustable and which typically may be of the order of hours, continues until the voltage across the capacitor drops below a second predetermined threshold level resetting the bistable flip-flop. The reset operation triggers a switch means for illuminating a lamp which indicates that a prolonged period of time has occurred since the last pump operation. Recharging of the capacitance does not occur until the pressure switch again undergoes a switch closure operation which automatically sets the bistable flip-flop and turns the lamp off. Operation of the circuitry so as to charge the capacitor rapidly and allow for a slow discharge rate serves to substantially reduce capacitance leakage problems.

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Cham, Switzerland

August X Sidler